1. Field of the Invention
The present invention relates to a method of erasing thermally printed data of a rewritable card and an apparatus for carrying out the same. More particularly, the present invention is concerned with improvement of the printed data erasing method for the rewritable card and the apparatus therefor in which one and the same thermal head is employed for thermally printing and erasing data.
2. Description of Related Art
Printed symbols such as, for example, characters, signs, images, graphics and/or the like (hereinafter referred to as the printed data) recorded on a rewritable card with the aid of a thermal head can be erased by heating the area where the printed data are resident up to a temperature which is lower than the temperature level at which the thermal printing has been performed. For example, a card comprised of a recording layer containing a leuco base or dye supported on a support is known as having such characteristics. As the heating means dedicated to the erasure of the printed data, there have heretofore been employed a heat applying plate, a heating roller, a thermal bar or the like. However, from the standpoint of decreasing the manufacturing cost of the rewritable card read/write apparatus and realizing the same in a miniature structure, approaches have been made for developing methods of erasing the thermally printed data of the rewritable card by using the very thermal head itself in place of the erasure dedicated device such as those mentioned above. As one of the methods, there can be mentioned a method according to which the thermal head is electrically energized in an erasure-dedicated step provided additionally and separately from the printing step. Other printed data erasing method for the rewritable card is what is referred to as the overwrite method according to which the data erasing operation and the data printing operation are carried out in one and the same cycle or stroke.
In this conjunction, it is however noted that the thermal head is intrinsically so designed as to heat locally a region of smaller area when compared with the area heated by the heating means dedicated to the erasure of the printed data. Consequently, when a rewritable card is so fed that a printed erasing range thereof is caused to move underneath the thermal head only once at a speed substantially corresponding to an ordinary card feeding speed as in the case of the typical apparatuses known heretofore, difficulty is encountered in allowing the heated card portion to be cooled gradually or slowly (i.e., at a low rate) so that discoloration of the data dot area can occur sufficiently. Besides, the discoloration characteristic of the rewritable card may undergo the influence of the ambient temperature. For these reasons, there exists a problem that some data fragments are likely to remain as the residue even after the data erasing process. Same holds true for the overwrite-type printed data erasing method.
In order to evade such poor effectiveness of the gradual or slow cooling of the rewritable card after passing by the thermal head or to prevent speedy cooling (i.e., cooling at a high rate) of the rewritable card, it is conceivable to control the feeding speed of the rewritable card such that the printed data erasing range or region of the rewritable card can move beneath the thermal head at a relatively low speed. In that case, however, the time taken for executing all the requisite processings on the card or the time taken until the card inserted into the apparatus by a user or customer is discharged therefrom, to say in another way, will become extremely long, giving rise to another problem. By way of example, the time taken for executing all the requisite processings will usually range from seven to ten seconds when the erasure-dedicated heating means is employed. By contrast, in the case of the single-cycle printed data erasing method or the overwrite-type printed data erasing method in which the thermal head is employed for both the printing of data and the erasure thereof, the processing time will amount to as long as ten to fifteen seconds.